Hardware Partition Layout & Dual-Slot A/B Boot Model

This document details the eMMC physical partition layout, the hardware A/B slot mechanics, and the persistent storage architecture used by Creality X2000 devices (Ender-3 V3 KE and Nebula Pad).

1. Physical Partition Table

The onboard eMMC is partitioned with a standard GPT partition table:

Partition	Label	Fixed Capacity	Mount / Role	Active Slot 1 (Stock)	Active Slot 2 (OpenKE)
`/dev/mmcblk0p1`	`ota`	1 MiB	Boot marker storage	Stores `ota:kernel` or `ota:kernel2`	Shared
`/dev/mmcblk0p2`	`sn_mac`	1 MiB	Factory serial & MAC addresses	Read-only identity	Shared
`/dev/mmcblk0p3`	`rtos`	4 MiB	Aux RTOS firmware (Slot 1)	Active	Inactive
`/dev/mmcblk0p4`	`rtos2`	4 MiB	Aux RTOS firmware (Slot 2)	Inactive	Active
`/dev/mmcblk0p5`	`kernel`	8 MiB	Linux uImage (Slot 1)	Active	Inactive
`/dev/mmcblk0p6`	`kernel2`	8 MiB	Linux uImage (Slot 2)	Inactive	Active
`/dev/mmcblk0p7`	`rootfs`	500 MiB	SquashFS rootfs (Slot 1)	Active	Inactive
`/dev/mmcblk0p8`	`rootfs2`	500 MiB	SquashFS rootfs (Slot 2)	Inactive	Active
`/dev/mmcblk0p9`	`rootfs_data`	300 MiB	Ext4 writable overlay	`/overlay`	`/overlay`
`/dev/mmcblk0p10`	`userdata`	~6.1 GiB	Ext4 persistent storage	Mounted at `/usr/data`	Mounted at `/usr/data`

2. Boot Selection via the OTA Marker

The bootloader (U-Boot) reads the 1 MiB ota partition (/dev/mmcblk0p1) on power-up to decide which kernel and rootfs to mount. The partition contains a simple ASCII string:

ota:kernel \rightarrow Boots Slot 1 (Stock CrealityOS: kernel p5, rootfs p7).
ota:kernel2 \rightarrow Boots Slot 2 (Custom / OpenKE: kernel p6, rootfs p8).

How Stock OTA Updater Flashes to Slot 2

When you run a USB update from the stock Creality touchscreen:

Stock firmware queries which slot is currently running (local_get_kernel_dev_path).
Since the printer is running on Slot 1 (ota:kernel), the updater targets the inactive slot:
- Flashes xImage to kernel2 (mmcblk0p6).
- Flashes rootfs.squashfs to rootfs2 (mmcblk0p8).
- Flashes zero.bin to rtos2 (mmcblk0p4).
Calls local_set_next_boot_device, which writes ota:kernel2 into mmcblk0p1.
Reboots into OpenKE.

Note

Stock firmware in Slot 1 (mmcblk0p5 and mmcblk0p7) is never overwritten by this process.

3. Persistent Data Isolation (`/usr/data`)

/dev/mmcblk0p10 is the single shared ~6.1 GiB persistent partition mounted at /usr/data. Both Slot 1 and Slot 2 share this partition, but they use strict directory separation:

/usr/data/
├── creality/            # Stock CrealityOS files (gcode, logs, userdata, factory data)
│   ├── userdata/
│   └── printer_data/
└── openke/              # OpenKE isolated runtime
    ├── apps/            # Mutable checkouts (klipper, moonraker, mainsail)
    ├── envs/            # Python virtual environments
    ├── system/          # Boot logs, activation state, machine configs
    └── printer_data/    # Klipper config (printer.cfg), macros, Moonraker DB

Because OpenKE namespaces all its data under /usr/data/openke/, flashing OpenKE does not erase or corrupt stock print history, WiFi credentials, or factory calibration files.

4. Reverting to Stock Firmware

If you ever wish to return to stock CrealityOS, you do not need to reflash. You simply toggle the boot marker back to Slot 1:

From OpenKE Shell (SSH)

echo -n "ota:kernel" > /dev/mmcblk0p1
sync
reboot

From Stock CrealityOS (if toggling forward again)

. /etc/ota_bin/ota_utils.sh
. /etc/ota_bin/ota_local_method.sh
local_set_next_boot_device
reboot

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